Given that SPT is not an exact science:
Should one apply a borehole diameter correction factor, CB (other than 1.0) when determining the N60 value, if mud-rotary methods are used?
My understanding is that it is used to account for stress relief in the larger diameter borings due to overburden...
I interpret the definition in ASCE 7 for 'service loads' to indicate that they apply solely to the serviceability state (e.g., settlement) and not the ultimate limit state (e.g., bearing capacity) in geotechnical design. Is my interpretation correct?
SERVICE LOADS: Loads imparted on a building...
How deep should a boring extend when areal fill is placed on a site of deep sand or clay?
For square and strip footings, depths of 2B and 6B would extend to isobar of 0.1q; however, for areal fill, what is prudent depth?
How are the Bousinesqq stress distributions influenced by shallow hard/dense layer like shallow rock?
Are they still applicable or do other factors need to be considered for assigning an influence factor?
Attached is a textbook example.
It appears to be a fictitious soil.
For example: If it has a su of 200 kPa it does not have a cohesion of 5 kPa.
My suspicion is that undrained strength always controls bearing capacity for clayey soils,
even though textbooks will often state that drained may...
According to your example, the bearing pressure would have triangular distribution, but that would not
be the same as the contact pressure, which is exactly my point.
My point is that bearing pressure is load/area of application.......so is uniform because that is how it is defined q = P/A.
Contact pressure is certainly not uniform...usually.
So, I disagree, I say they are different in that regard, but the same in quantity.
Integral of contact pressure...
Is bearing pressure the same as contact pressure?
Are these terms/concepts separated by soil structure interaction?
For example, if I have a box that is 10ft x 10ft in plan, 1-ft height fill with water, bearing pressure exerted will be 62.4 psf.
But because the ground responds uniquely, the...
I've seen statements to the effect that the long-term (effective stress) values for heavily oc clay result in a lower bearing capacity than would be achieved using undrained (total stress) parameters. Dilation and development of negative pore water pressure are mechanisms for decreased shear...
I would love to see this approach as compared with reducing the center settlement of a rigid foundation by 15%.
My guess is that they are probably very similar; and trying to split hairs is not warranted for small spread ftg. evaluations.
…...certainly for a flexible mat, this approach seems...
I am not chasing accuracy here.
I am trying to determine if the use of rigidity factors for reducing the settlement of a rigid foundation (where settlement was estimated at its center assuming the foundation was perfectly flexible)
is appropriate. Assuming somewhat uniform soils, the settlement...
Thanks Ron,
I appreciate all of your posts. I also agree that trying to get accurate with settlement predictions is probably a lost cause.
With regard to rigidity factors, it doesn't appear that most are familiar with this concept; which is what I kind-of suspected.
They are presented often in...
Settlements estimated below the center of a flexible footing will be more than for a rigid footing. The rigidity factors account for this since the rigid footing cannot settle as much at the center, although it wants to. More info. on rigidity factors is attached.
I am still curious to know...
I'm not sure this answers the specific question. Are rigidity factors appropriate?
The answer is no if using schertmann's method...reason why (not sure), method is for flexible footings; why not reduce settlements for 4x4 rigid ftg using this method?
Not sure why rigidity factors would not...
EireChch,
I am unclear on why rigidity factors cannot be applied if using the Schmertmann method.
Wouldn't that be the point, to convert from flexible to rigid behavior??
Please provide rationale.
I am curious if anyone uses these routinely for settlement calculations.
If someone needs more context, I'm guessing they are not using very much...….which answers my question.
The concept seems appropriate; just not sure why I don't hear of many who use this technique???
Ron,
The use of rigidity factors seems to be similar to the use of a characteristic point as described in
'Basics of Foundation Design'; by Fellenius. The concept seems appropriate and not overly conservative
in my opinion unless you can convince me that there will be more settlement at the...
